Long-term variability of solar irradiance and its implications for photovoltaic power in West AfricaIna Neher1,2, Susanne Crewell2, Stefanie Meilinger1, Uwe Pfeifroth3, Jörg Trentmann3

1 University of applied science Bonn-Rhein-Sieg, 2 University of Cologne, 3 German weather service (DWD)

Contact: ina.neher@h-brs.de

Neher et al. (2020), submitted to ACP

1 Solar power for West Africa• Solar power can serve the rising global energy demand

with low environmental impact.• West Africa is rich in global horizontal irradiance (GHI)

and power generation is lacking.• Satellite data for GHI can serve as input for a linear

photovoltaic (PV) power model, processed withmeasured data (see Fig. 1).

3 PV potential between 1983 and 2017 and trends• High potential in Sahel region and Sahara (GHI > 250 W/m2 ,

Fig. 3 a); PV yield > 5 kWh/kWp, Fig. 4 a).• Positive trend of GHI in the Sahara, marginal trend in Sahel

zone and negative trend in Southern West Africa (Fig. 3 b).• Positive trend of GHI mainly during dry season (October to

April, Fig. 3 c).• Negative trend of GHI mainly during wet season (Mai to

September, Fig. 3 d).

2 Surface Solar Radiation Data Set - SARAH-2.1• Satellite retrieval of GHI in a daily resolution between

1983 and 2017.• Comparison of satellite data to measurements in

Agoufou (Mali), Banizoumbou (Niger) and Djougou(Benin) (Fig. 2, AMMA dataset).

• RMSE: 20 - 34 W/m2; better agreement in Agoufou andBanizoumbou than in Djougou.

• Normalization of GHI with minimal daily zenith to modelPV power.

4 Conclusion• Decrease of GHI during wet seasons (likely due to the

increase of cloud cover) and increase during dry season(likely due to lower dust movement and clouds).

• PV potential increased over time in regions with low urbandensity and decreased in regions with high urban density.

• For a solar based electricity system in West Africa, North-South grid and seasonal storage capacities are needed.

Fig. 1: Daily PV yield as a function of normalized GHI combining the

calculations at three measurement sites

and for three temperature levels, T ≤ 30°C (blue), 30°C ≤ T ≤ 35°C (green), T

≥ 35°C (red).

Fig. 2: Comparison of simulated and observed GHI as daily averages at

three locations, a) Agoufou, b) Banizoumbou and c) Djougou. The

ΔAOD (indicates the difference between the measured AOD and the

climatological AOD used for the SARAH retrieval) is indicated as color.

a)

c)

b)

Fig. 4: Mean PV yield at each latitude, for the total year (a) as well as for the dry (dark) and wet (light)

season (b), in the longitude range between 4°W and 4°E. The points in (a) mark the mean PV

yield calculated with explicit model at Agoufou

(2005-2008), Banizoumbou (2005-

2012) and Djougou (2002-2009).

a)

b)

Fig. 3: Mean GHI (a) and linear trend for all seasons (b), the wet (c) and the dry season (d) between 1983 and 2015.

a) b)

d)c)